Abstract: Modern River Deltas: Variability of Processes and Sand Bodies

James M. Coleman

Subsurface deltaic sand bodies have produced considerable quantities of hydrocarbons, yet their variable geometry and interfingering relations have not been studied systematically. Delta facies result from interacting dynamic processes (climate, hydrologic regime, wave energy, tidal action, etc.) which modify and disperse transported riverine sediments. Similar process and form parameters were compared in 50 modern deltas to investigate the differences between the deltas and to generate distinctive deltaic frameworks. The most significant processes, in a geologic sense, are climate, water-sediment discharge, river-mouth processes, nearshore wave power, tidal regime, nearshore currents and winds, shelf slope, tectonics of the receiving basin, and receiving-basin geometry. o one delta model could be formulated for use as a basis for predicting vertical sequences in all deltas, and six distinctive delta models and their stratigraphic framework have been established. The study indicated that delta/sand-body distribution, geometry, and internal characteristics are primarily a function of wave-energy distributions, river-mouth dynamics, subsidence, and longshore currents. The following modern deltas illustrate the common deltaic vertical sequences: (1) Mississippi delta (USA)--low wave energy, low tide, temperate climate; (2) Klang delta (Malaysia)--low wave energy, high tide and currents, tropical; (3) Ord delta (Australia)--low wave energy, extreme tide, arid; (4) Burdekin delta (Australia)--intermediate wave energy, high tide, semi-arid; (5) Sao Francisco d lta (Brazil)--high wave energy, low currents, dry tropical; (6) Senegal delta (Senegal)--extreme wave energy, high currents, arid.

AAPG Search and Discovery Article #90973©1976-1977 AAPG Distinguished Lectures